1. Field of the Invention
This invention relates to lens wafers and more particularly to a polymer composition for coating at least one surface of the lens wafer in order to provide a means to clean the wafer as well as to form a protective and removable film thereon.
2. State of the Art
Eyeglass lenses have traditionally been formed as a single integral body of glass or plastic. Grinding or molding such lenses to meet the specifications of a particular prescription requires costly equipment, highly skilled technicians and is time consuming.
It has recently been found that the fabrication of ophthalmic lenses can be economically accomplished in a more rapid manner with a laminated lens construction in which two lens wafers are bonded together with a transparent adhesive. Such lens wafers are described, for example, in U.S. Pat. Nos. 5,149,181, 4,857,553, and 4,645,317 and British Patent Application, publication number 2,260,937A which are incorporated herein by reference in their entirety.
The laminate construction enables assembly of composite lenses having any of a large number of different combinations of optical corrections from a relatively small stock of prefabricated lens wafers of different configurations. Pairing of different combinations of a front surface lens wafer with a back surface lens wafer can, for example, provide composite lenses having any of a large number of different powers as the power of the lens is the summation of the powers of the two wafers. Such combinations provide for a large majority of all of the prescriptions required for clear vision.
Notwithstanding the advantages of using lens wafers in the construction of a composite lens, a problem arises with the use of such lens wafers. Specifically, any contaminates such as dust, dirt, fingerprints and moisture found on the wafer surfaces to be glued will become permanently entrapped at the interface of the wafers in the composite lens upon adhesion of the front wafer to the back wafer resulting in defects in the lens. These defects reduce the optical quality of the finished lens and can ultimately lead to lens rejection.
Accordingly, in order to provide a defect-free composite lens, the wafer surfaces to be laminated together (with a transparent adhesive) should be substantially clean of such contaminates. However, since the wafers are invariably handled during composite lens fabrication, it is particularly difficult to avoid contaminates such as fingerprints and dust on the wafer surface interface.
The ability to maintain a contaminant-free surface is also critical if optical coatings such as anti-reflection coatings are to be applied. Again, any surface damage or contamination will be uncorrectable after application of the optical coating.
Previous methods known in the art neither address nor are applicable to this problem. For example, U.S. Pat. Nos. 3,899,315 and 3,899,314 relate to texture control of glass ophthalmic lenses by use of a protective layer which is removed prior to use. Here, a flat glass lens preform is provided with a thin protective layer of a chemically soluble glass fused thereto. In the manufacturing process, the flat preform is subsequently cut and pressed or slumped to the desired ophthalmic shape and the protective layer subsequently removed by dissolving this in a corrosive reagent, thereby exposing the underlying surface which, while smooth, nevertheless needs to be cleaned. The lens is rendered immediately adaptable to ophthalmic use, without further working (grinding, polishing or cleaning) of the surface. This wet process, however, is not suitable for reagent sensitive molded plastic (e.g., polycarbonates or polymethacrylates) lenses. Furthermore, it has been found that the wet process does not provide a sufficiently clean surface on lens wafers required for laminated ophthalmic lenses.
Another unrelated prior art approach to removing dust and grease from a polymer surface is disclosed in U.S. Pat. No. 4,199,375 which describes a method for removing dust and grease from phonograph records by applying a polyvinyl alcohol composition which forms a self-supporting film upon drying. When the film is lifted from the record, dust and grease, which are dissolved in the film, are removed. However, this composition, when applied to plastic lenses or lens wafers, forms films that are difficult to remove.
In view of the above, it would be particularly desirable to provide a means to effectively clean the surface of lens wafers prior to adhering this surface to another surface during fabrication of a laminated lens or application of a coating (e.g., an anti-reflection coating) to the wafer surface.